(i) Field of the Invention
The present invention relates to an electromagnetic clutch for transmitting power from a power source of a vehicle to a compressor of an air conditioner for vehicle, for example.
(ii) Description of the Related Art
A generally known electromagnetic clutch includes a first rotor rotated by power from outside, an armature plate arranged oppositely to one end face of the first rotor in the axial direction, an electromagnetic coil for attracting the armature plate to the first rotor side, a second rotor for transmitting a turning force transmitted from the armature plate side to a driven shaft on a driven device, and a plurality of plate springs in which one end side is connected to the armature plate and the other end side is connected to the second rotor for transmitting the turning force from the armature plate to the second rotor and for urging the armature plate in the direction away from the first rotor.
In the above electromagnetic clutch, the armature plate and the first rotor are connected only with a magnetic force of the electromagnetic coil. Therefore, it is necessary to enlarge the electromagnetic coil so as to increase a torque capacity which can be transmitted between the first rotor and the armature plate. That is, it is not possible to reduce weight and power consumption of the electromagnetic clutch.
On the other hand, an electromagnetic clutch for which the above point can be improved is provided with a first rotor similar to the above, not shown, an electromagnetic coil, not shown, an armature plate 61, a second rotor 62, and a plurality of plate springs 63 in which one end is connected to the armature plate 61 and the other end is connected to the second rotor for transmitting the turning force from the armature plate 61 to the second rotor 62 and for urging the armature plate 61 away from the first rotor (See FIGS. 13 to 15). To each of the plate springs 63, a compression force is applied between its one end and the other end when the turning force is to be transmitted. An inclined portion 63a is provided on the plate spring 63, which is formed by bending a part thereof to the first rotor side. A part of the compression force applied to the plate spring 63 acts as a force for pressing the armature plate 61 onto the first rotor by the inclined portion 63a. 
However, in the latter electromagnetic clutch, a bent portion 63b of the plate spring 63 is deformed in the direction away from the first rotor by reaction of the pressing when the compression force is applied to the plate spring 63 and the armature plate 61 is pressed onto the first rotor. Since a stress is concentrated to the bent portion 63b by this, the stress needs to be alleviated.